Electrolytic cell for alkali metal chlorates

ABSTRACT

ELECTROLYTIC CELL INCLUDES PAIRS OF FLAT PERFORATE CATHODES ASSEMBLED IN FIXED SPACED APART DISPOSITION OUTSIDE THE CELL TO DEFINE MODULES OF OPEN-ENDED BOXLIKE CONFIGURATION WHICH ARE THEN WELDED TO THE CELL TANK WALLS. A COATED METAL ANODE IS RECEIVED BETWEEN EACH CATHODE PAIR, CHEMICALLY RESISTANT INSULATIVE GUIDES AND SPACERS PROVIDING SLIDABLE INTERELECTRODE CONTACT TO ASSURE EXACT GAP SYMMETRY FOR THE HEADBOARD SUSPENDED ANODES. ELECTRODE POWER BUSES OF THIN SECTION AND EXTENDED SURFACE INITIMATELY CONTACT THE HEADBOARD AND TANK SURFACES. FLOODED CELL OPERATION EFFECTS COOLING OF THE BUSES.

July 16, 1974 J. R. H ODGES 3,324,172

ELECTROLYTIC CELL FOR ALKALI METAL CHLORATES Filed July 18, 1972 4Sheets-Sheet 1 July 16, 1974 J. R. HODGES 3,324,172

ELECTROLYTIC CELL FOR ALKALI METAL CHLORATES Filed July 18, 1972 4Sheets-Sheet 60 I 64 7 J0 F y ZR Z I 73 July 16, 1974 .1. R. HODGES3,324,172

ELECTROLYTIC CELL FOR ALKALI METAL CHLORATES 4 Sheets-Sheet 3 Filed July18, 1972 United States Patent Oflice 3,824,172 Patented July 16, 19743,824,172 ELECTROLYTIC CELL FOR ALKALI METAL CHLORATES Jimmie RayHodges, Benton, Ky., assignor to Penn-Olin Chemical Company, Wilmington,Del. Filed July 18, 1972, Ser. No. 272,830 Int. Cl. B01k 3/00 US. Cl.204-269 Claims ABSTRACT OF THE DISCLOSURE Electrolytic cell includespairs of flat perforate cathodes assembled in fixed spaced apartdisposition outside the cell to define modules of open-ended boxli'keconfiguration which are then welded to the cell tank walls. A coatedmetal anode is received between each cathode pair, chemically resistantinsulative guides and spacers providing slidable interelectrode contactto assure exact gap symmetry for the headboard suspended anodes.Electrode power buses of thin section and extended surface intimatelycontact the headboard and tank surfaces. Flooded cell operation effectscooling of the buses.

This invention relates to an electrolytic cell, and more particularlyrelates to a diaphragmless electrolytic cell which is especially adaptedfor manufacture of alkali metal chlorates; e.g., sodium chlorate.

In recent years, much effort has been directed toward the development ofimproved electrodes for operation of electrolytic cells. The traditionalgraphite anodes which are consumed with use are now being replaced withcoated metal anodes, normally a valve metal, such as titanium coatedWith a platinum group metal or metal oxide. The longer life and improvedvoltage characteristics of such metal anodes has effected substantialsavings in power and maintenance costs.

The present invention advantageously utilizes these dimensionally stablecoated metal anodes to construct a diaphragmless monopolar cell of verysimple geometry which is conducive to facility in fabrication. Theconcept of the instant system is modular in nature to afford greatflexibility in sizing so as to enable design to a specific productionload. The cathodes employed in this electrolytic cell are foraminous inconstruction thus leading to improved current efficiency. The perforatedconstruction of the cathodes provides a stable configuration whichresults in consequent reduction in oxygen formation. The cell isoperated in flooded condition and the evolved gases are drawn off withthe liquid electrolyte through a single opening in the headboard so asto reduce the volume of gas within the cell itself and thereby diminishlikelihood of explosion and hazards associated with sparking or shortcircuits. The cell walls form part of the electrical circuit, theelectrode buses being of relatively thin section and extended surface inintimate contact with the exterior walls of the cell tank and headboardso as to permit cooling by the electrolyte being pumped through thecell.

It is therefore an object of this invention to provide an electrolyticcell having greatly improved operating characteristics.

Other objects of this invention are to provide an improved device of thecharacter described that is easily and economically produced, sturdy inconstruction and highly efiicient and effective in operation.

With the above and related objects in View, this invention consists ofthe details of construction and combination of parts as will be morefully understood from the following detailed description when read inconjunction with the accompanying drawings in which:

FIG. 1 is a side elevational view of an electrolytic alkali metalchlorate cell embodying this invention.

FIG. 2 is a top plan view thereof.

FIG. 3 is an end view of the cell.

FIG. 4 is a top plan view, and partly broken away to show the interiorof the cell.

FIG. 5 is a sectional view taken along lines 5-5 of FIG. 4.

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 5.

FIG. 7 is a perspective view of an anode plate embodying this invention.

FIG. 8 is a sectional view taken along lines 8-8 of FIG. 4.

Referring now in greater detail to the drawings in which similarreference characters refer to similar parts, there is shown anelectrolytic cell for electrically producing alkali metal chlorates, forexample sodium chlorate, from alkali metal chloride brines. The cellincludes substantially rectangular tank or container 10 which isfabricated of a structurally suitable electrically-conductive material,such as hot rolled carbon steel plate. The tank 10 has side walls 12 and14, end walls 16 and 18, and a closed bottom 20 all welded along theadjacent edges. Dielectric pedestals 22 act as supporting legs andinsulate the tank from the ground. A flanged fitting 24 is coupled to apiping system (not shown) which pumps the brine feed from storage tanksinto the cell. Pipes 26 distribute the electrolyte uniformly through thelower portion of the tank 10. Heat generated in the cell may be removedeither by cooling the recirculating liquor in an external heat exchangeror by pumping cooling water through internal coils (not shown).

Cathodes C are fabricated in pairs outside the cell to form modularunits having an open-ended boxlike configuration, the. modulesthereafter being welded to the cell interior. Each cathode C comprises ahot rolled carbon steel plate having a plurality of slots 28. The slots28 are shown oriented vertically in a diamond-shaped configurationalthough other suitable perforate constructions may be provided in theform of expanded metal, mesh or screen, or interlaced strips, or rods orbars. Ap proximately 20 to 30 percent open area is provided to act as arelief for the gases evolved during electrolysis thus promoting currentefficiency. However, suflicient cross section of metal is retained so asto maintain current carrying capability. Vertically spaced distributorbars 30 are welded to the back of each cathode C in order to shorten thecurrent path and to act as reinforcing stiffening ribs. The lateraledges of each cathode C are welded along seams 32 on opposite sides ofthe tongues of rabbeted steel bars 34, the latter being coextensive inlength with the cathode height. The bars 34 act as spacers formaintaining the cathodes of each module pair in fixed apart dispositionto enable reception of the anodes A therebetween. The cathode modulesare then secured to the interior of the tank 10 by welding the spacerbars 34 to the end walls 16 and 28 along seams 36. Stringers 38 arewelded transversely along the bottom edge of the assembled cathodemodules to provide further reinforcement and to act as stops to preventa suspended anode from falling upon the cell bottom 20 should any anodebe accident-ally disconnected. L-shaped clips 40 of a suitableelectrically insulative and chemically resistant material, such aspolyvinylidene fluoride or polytetrafluoroethylene, are secured byscrews 41 along the upper edge of the cathodes C in longitudinallyspaced disposition with each other. The insulator clips 40* act as guidestand-offs for the anodes A when the latter are inserted within theboxlike cathode modules and in addition prevent short circuiting in theevent of failure of an anode suspension.

A flange 42 is welded to the outer perimeter of the tank along the upperedge thereof, and a suitable chemically-resistant and insulative gasketseal 43 applied to the upper surface of the flange and the inner marginsof the tank walls adjacent thereto. A conductive headboard 44,preferably of titanium or titanium alloy plate or clad construction, isthen mounted upon the flange 42 by insulator bolts 46 to define a lidfor the tank and a suspension for the anodes A. Such a clad constructionmay be sandwich of steel explosively bonded between outer layers ofcopper and titanium.

The anodes A are flat plates of generally rectangular configuration andpreferably fabricated of a valve metal, such as titanium, which iscoated on both sides with a platinum group metal or metal oxide. A bar48 of enlarged cross section is welded along the upper edge of theanodes A in order to improve current distribution. A circular pressurefoot 50* having a flanged shoulder in which is supported an O-ring 52 iswelded to the upper central portion of the distributor bar 48. A highlyconductive stud 54 is threaded into registering tapped holes in thepressure foot 50 and the distributor bar. The preferred material for thedistributor bar 48 and the pressure foot 50 is again titanium or analloy thereof. The anodes A are suspended by passing the studs 54through holes in the headboard 44 and threading nuts 56 over the exposedends of the studs. The O-ring 52 becomes compressed against the innersurface of the headboard 44' to form a gasand liquid-tight seal. Alongitudinally slotted cylindrical insulator 58 of chemically resistantmaterial, such as polyvinylidene fluoride, is secured to the lower edgeof each of the anodes A by non-conductive, corrosionresistant dowel pins60. The insulators 58 have a diameter which provides a sliding fit withthe opposed surfaces of the paired cathodes in each module, as bestshown in FIG. 6. Thus, a set of three anodes A, for example, areinserted within each module by passing the insulators 58 through thespaced guide clips 40 at the upper edge of the openended cathode 'box.The guides 40' and the insulators 58 assure accurate symmetrical spacingof the surface of the anodes with respect to the opposed surfaces of thecathode pairs. The electrode pattern of the foregoing cell iscathode-anode-cathode cathode-anode-cathode-cathodeanode-cathode Currentis directed to the anodes A through the studs 54. A thin metal plate 60of a highly conductive material, such as aluminum or copper, having anextended surface is interposed in face to face contact with the uppersurface of the headboard 44 and acts as an anode bus. The abutting facesof the bus 60 and the headboard 44 are highly polished to permitintimate contact with each other. Upstandin-g screws 62 threaded withintapped holes in the headboard pass through registering holes in theanode bus 60, and nuts 64 tie the bus securely to the face of theheadboard. Since the conductor 60" presents a relatively large surfacefor dissipation of heat, the cross section may be reduced accordingly.Conductor terminals 66 are secured to the bus 60* in a, conventionalmanner and serve as a means for connecting the anodes A to the positiveside of a high amperage DC. power supply lead 67.

The negative side of the DC. power source is coupled to the cathodes Cin a similar manner. Relatively thin U- shaped buses 68 and 70 of copperor aluminium conductor are suitably attached to the walls 14, 16, and 18in intimate contact therewith as by welding or brazing. Strip terminals72 are utilized to couple the cathode buses 68 and 70 to lead 74 at thenegative side of the DC. power supply. As in the case of the anode bus60, the surface area of the cathode bus strips 68 and 70 is extended tocover a goodly portion of the tank walls, and because of the ability ofthe expanded surface to dissipate heat, the total metal conductorrequirements are accordingly reduced with consequent reduction inthickness. By virtue of the bus configuration, current is permitted topass through rather than along the cell walls thereby reducing powerloss through less conductive metals. Accordingly, the cell walls may bedesigned in accordance with mechanical rather than electricalconsideration.

Finally, the discharge of the electrolyte being pumped into the cell isthrough a pipe fitting 76 incorporated in the headboard 44. This causesthe cell to be operated in flooded condition such that the electrolyteis being constantly wiped across the interior surfaces of the headboard44 as well as the tank 10 thus enabling the cell itself to function as aheat exchanger. In this manner, the cell liquor which may be at atemperature of to F. acts to cool the walls of the cell and theheadboard. Consequently, the anode and cathode buses 60, 68 and 70 whoseextended surfaces are in intimate contact with the cell per se andoperating at a temperature of perhaps 300 F. can be reduced in mass byvirtue of the external air cooling and the internal liquid cooling. Thedischarge of liquor from the pipe fitting 7 6 is then directed to aspecially designed external degasser 78 after which the chlorate isseparated from the chloride salt by conventional evaporative,crystallizing and centrifuging techniques.

In assembling the cell for operation, the anodes A are inserted betweenthe cathodes C until the shoulder of the distributor bar 48 sits uponthe guide stops 40. During insertion, the cylindrical insulator 58 makesslidable contact with the adjacent cathode surfaces and the guides 40slidably engage the opposing anode surfaces thereby insuring equal andprecise interelectrode gaps. Since the insulators 58 and the guides 40are of non-metallic materials, danger of scratching the coatings in theanodes is avoided. As is apparent, the modular concept permits greatflexibility in design while the extended surface configuration of theelectrode buses forming a part of the cell walls allows operation athigher temperatures and greater current densities.

Although this invention has been described in considerable detail, suchdescription is intended as being illustrative rather than limiting,since the invention may be variously embodied, and the scope of theinvention is to be determined as claimed.

What is claimed is:

1. An electrolytic cell for producing an alkali metal chlorate from analkali metal chloride brine comprising:

a tank;

a plurality of substantially flat hollow cathodic modules supported insaid tank in horizontally spaced apart disposition with respect to eachother, each module being of generally boxlike configuration having anopen top and bottom with horizontally spaced apart cathode plates, theupper and lower edges of said cathode plates being respectively spacedvertically from the top and bottom of said tank;

a generally flat anode suspended within each cathodic module in equallyspaced disposition between the cathode plates thereof, the lower edge ofeach anode terminating substantially coextensive with the lower edge ofthe corresponding cathode module while the zones between adjacentcathodic modules are devoid of anodes so as to define an electrodepattern;

cathode-anode-cathode-cathode-anode-cathodecathode-anode-cathode meansfor applying a DC. power source across said anodes and said cathodemodules;

means for introducing the alkali metal chloride brine into the tank soas to submerge the anodes and cathodes, and means for Withdrawing alkalimetal chloride-chlorate liquor from said tank after the brine has beensubjected to electrolysis.

2. The electrolytic cell of claim 1 wherein each of said cathodes is offoraminous construction.

3. The electrolytic cell of claim 2 including conductive memberscoextensive with said cathodes interconnecting the respective adjacentlateral edges of the cathodes in each module, and means for afiixingsaid conductive members to the opposing side walls of said tank so thatthe cathodes are oriented in vertical disposition with the lower edgesof the cathodes spaced from the bottom of said tank.

4. The electrolytic cell of claim 3 including a headboard enclosing saidtank and suspending each of said anodes, and means for insulating saidheadboard from said tank.

5. The electrolytic cell of claim 4 including a generally cylindricalinsulative member afiixed to the bottom of each anode and having adiameter effecting a sliding fit intermediate adjacent cathodes of eachmodule.

6. The electrolytic cell of claim 5 including insulative clips at theupper edges of the cathodes in each module slidably engaging theopposite surfaces of the anodes suspended therebetween.

7. The invention of claim 4 including thin strips of material of highelectrical and thermal conductivity in intimate face-to-face contactwith a substantial portion of the exterior surfaces of said headboardand said tank sidewalls respectively to define buses for electricalpower.

8. An electrolytic cell comprising:

an electrically conductive tank;

cathode means in said tank and electrically coupled thereto;

an electrically conductive headboard constituting a lid for said tank;

means for electrically insulating said headboard from said tank;

anode means suspended from said headboard in adjacently spaceddisposition with said cathode means; means for pumping an electrolytethrough said tank intermediate said anode means and said cathode meansto maintain the cell in flooded disposition with the electrolyte incontact with substantially the entire interior surface of said tank andsaid headboard; an anode bus electrically connected to said anode means,said anode bus being of strip material of high conductivity and havingan extended surface area in intimate face-to-face contact with theexterior surface of said headboard, a cathode bus formed of stripmaterial of high conductivity and having an extended surface area inintimate face-to-face contact with the exterior surface of said tank, sothat the electrolyte being pumped through the cell acts as a heatexchange medium to cool the respective anode and cathode buses via theheadboard and tank thereby enabling reduction in the amount of busmaterial re quired for a given power load; and

means for applying a D.C. power source across said anode bus and saidcathode bus.

9. The electrolytic cell of claim 8 wherein a single electrolytedischarge from the cell is located in the headboard so that the cell canbe maintained in flooded condition to permit a safe exit of the cellefiluent liquor with the generated gases intimately entrained thereinwhereby danger from gas explosion is minimized.

10. The electrolytic cell of claim 9 including degassing means forseparating the entrained gases from the liquor efiluent.

References Cited UNITED STATES PATENTS 3,732,153 5/1973 Harke et a1 20l270 FOREIGN PATENTS 823,187 9/1969 Canada 204 JOHN H. MACK, PrimaryExaminer W. I. SOLOMON, Assistant Examiner US. Cl. X.R. 20495, 270

